Without seeing the crack, it sound as though it just may be an expansion problem - especially being around the bathroom. A handyman would just beat the cracks back with a simple hammer so the crack and ajoining area is below the existing wall plane, add some sheetrock nails where nailers are available - install tape, mud etc (tape and bed)- retexture and paint to match. Do not be surprised if the crack comes back in a few years. The second time you do it should be the charm. You did not mention anything along the termite scenario so we are ruling that out for now. A termite nesting area will bulge but will not crack as I am thinking you are trying to explain. After saying that, a picture would help out immensely.